Trace Elements in Untreated Wastewater in Central India: A Controversial Consideration for Irrigating Vegetables—To Employ or Not to Employ?

In peri-urban areas of developing countries, the use of untreated wastewater (UWW) for crop irrigation is a widespread practice driven by the severe lack of access to clean water. This practice may lead to the accumulation of heavy metals (HMs), which may pose significant risks to both human health and the environment. To address this issue, a comparative study was conducted across five sites utilising UWW and three control sites relying on tube well water. The research rigorously analyzed soil, water, and locally grown vegetables specifically brinjal, cabbage, spinach, and fenugreek in the peri-urban region, with a focus on examining the levels of HMs, including cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn). These HMs were quantified using inductively coupled plasma atomic emission spectrometry (ICP-AES). Results indicated that the concentrations of HMs in both soil and water samples remained within permissible limits established by regulatory agencies. However, notable variations in soil characteristics were documented; the soil pH decreased by 6.15%, suggesting an increase in acidity, while electrical conductivity surged by 83.75%, indicating elevated levels of soluble salts. Furthermore, soil organic carbon (SOC) levels experienced a significant increase of 42.45%. which can be linked to the prolonged application of UWW as a nutrient-rich irrigation source. In vegetable samples, the concentrations of HMs were generally within permissible limits. Chromium levels were found to exceed these limits, specifically in cabbage and brinjal, raising health risk concerns. It is recommended to avoid consuming cabbage and brinjal cultivated under the current conditions, as they may be affected by harmful HMs. Additionally, exploring the cultivation of alternative crops that do not absorb these harmful HMs would be beneficial. Multivariate statistical analysis confirmed UWW irrigation was the primary driver of HM contamination in the examined areas, highlighting an urgent need for improved water management practices. The bioconcentration factor analysis revealed a higher uptake of Fe and Ni in spinach. Assessments indicated that consuming these vegetables does not pose significant non-carcinogenic health risks. These results highlight the need for continuous monitoring and sustainable irrigation practices to protect public health and ensure agricultural productivity.